257 Roberts keyholing

It sounds unlikely, but the usual reason for keyholing is that the bullets are too small for the bore. (Yes, I remember the fellow whose rifle was shooting low and the bullets were bouncing into the target! A lot of us blew the analysis on that one!)

Jim

It's going to be necessary to slug the bore with #2 or #1 buckshot or something like that, to see where you stand on bore size, now that you have piqued our interest.

The way I see it, either the heavier bullets are not stabilizing because of the twist, or the bore is not exactly .257 (larger than?). The keyhole at 50yds is more telling than the 100yd keyhole. As others have noted, it may indicate a poor bullet to bore fit, but the jury is still out until we learn more.



NCsmitty

jimmyraythomason said:

It is in fact a 1:10 twist as per the cleaning rod/patch method. I haven't had the barrel slugged but a .257 bullet enters from the muzzle to just shy of the cartridge case mouth. I bought the barrel off Gunbroker.com unmarked but sold as a .257 bob barrel. I sent the barrel,receiver and stripped bolt to my smith for installation. I don't know if he verified it as a .257 barrel before installing and chambering it. He also cut a new crown. The crown looks perfectly centered.

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My Rem700 in .257rbts shoots those 117gr Win Power-Points very, very well...
I stuck one into the muzzle of my rifle as a comparison to your own test...
Here's a pic... mine certainly didn't go in to 'just shy of the case mouth' IMHO...

That's certainly looking like you've got a 6.5 or 7mm barrel then...

You are starting to scare me now!

That is not your answer.
You cannot simply stick another caliber ammo in it and hope for the best.

Your only course of action now is to first.
1. Slug the bore and find out what the measurement actually is.
Sticking a bullet in the muzzle tells you exactly nothing as every brand of bullet has a different ogive shape and will go in the hole further, or not as far.
The only actual bullet diameter that matters is all inside the case.

2. If it is in fact chambered for .257 Roberts, nothing else you can buy is going to headspace right.
It would be dangerous to try to shoot 6.5x57 Mauser in it.
It could have very excess headspace, no matter what the bore size is.

I would strongly suggest you take it back to the gunsmith who put the barrel on it.
Have him figure out what the bore size actually is by slugging it.

Only then can he decide how to best fix it.

rc

OK.

So, tell us why you thought this rifle was .257 Roberts in the first place?

The seller on Gunbroker should be eating the costs of this deal.

jimmyraythomason said:

Haha, At least it got your attention! I'm going to call the smith that did the work next week and talk it over with him. Actually,I'm hoping it is a 6.5 bore because I think I'd rather have a 6.5x55 than a .257 Roberts.

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If it really is a 1:10 twist, I think that's too slow for a typical 6.5x55 bullets. IIRC, they usually need a 8.5 twist.

Probably still make a good varmint gun with light bullets though.